1. Technical Field
The present invention relates generally to athletic equipment and, more particularly, to an adhesive bond for intercoupling segments of a modular shaft for athletic equipment.
2. Discussion
The design and performance of athletic equipment has advanced significantly over the past few decades. These advancements are attributable, at least in part, to the wide variety of materials from which such equipment is now manufactured. Oftentimes, these new materials are both lighter and stronger than the wood or steel used in the past for hockey sticks, tennis rackets, lacrosse sticks, polo mallets, golf club shafts, and the like. As a result, designers now have unparalleled opportunity to select an appropriate material for the specific design criteria that are important to such equipment.
A prime example of both the difficulties in design and the opportunities provided by new materials is the golf club shaft. The golf swing is a complex and high speed action wherein the shaft of the golf club is subjected to a variety of forces. The magnitude of these forces, their distribution along the shaft, and the desired performance characteristics of a golf shaft make shaft design a complex and difficult endeavor. A properly designed golf shaft balances a variety of parameters that impact the playability and feel of a golf club including the shaft's flexibility, strength, weight, and overall geometry. Notwithstanding the availability of new materials, it has proven difficult over the years to find materials that provide a proper balance of these and other parameters.
In order to accommodate the various design parameters of a golf shaft, some manufacturers have attempted to use different materials for different parts of the golf shaft. It was anticipated that this technique would allow designers to use the specific benefits of a particular material in the most applicable area of the shaft while using a different material in other areas. Despite the initial promise of this approach, difficulties in adequately coupling the two shaft segments have led to only limited success of multi-material or modular shafts.
When bonding shaft segments to one another it is important to create a strong and uniform bond. Various bonding techniques have been used within the art without adequate results. For example, shaft segments have been coupled to one another by wrapping resin impregnated wraps, commonly used to create composite shafts such as graphite shafts, over each segment. However, the bond strengths provided by the wraps have been inadequate and the overlap in the bond area has undesirable performance characteristics as well as being aesthetically unpleasing. Other attempts to bond shaft segments to one another, such as through the use of an adhesive (e.g. epoxy), have likewise been unsuccessful due, in part, to the difficulty in maintaining proper shaft alignment and achieving a sufficient and uniform bond about the shaft.
Another problem in the fabrication of modular shafts, present when metal shaft segments are used, is corrosion. Galvanic corrosion is particularly troublesome in steel golf shafts due to the difficulty in maintaining an adequate separation distance between the thin walled steel shaft segment and the adjoining shaft segment. The presence of moisture in the golfing environment heightens these corrosion concerns.
It should be appreciated that while a majority of the above discussion is presented with reference to golf club shafts, other athletic equipment shafts have similar design and performance difficulties.
In view of the above, it would be desirable to provide a bonding apparatus for athletic equipment handles and shafts that achieves a sufficient separation distance between adjoining shaft segments, an adequate and uniform bond about the segments, and that properly aligns the shaft segments. Such an apparatus would permit the effective use of multiple materials in a single athletic equipment shaft thereby allowing shaft designers to maximize the benefits achieved by each material.